When using the Split Screen feature, the audio of the camera on the LEFT screen will be played on the Parent Unit. The right-side camera will show the sound detection icon but will not transmit audio. 

If there is no sound from the left camera and the right one does, then the RIGHT camera’s audio will play as normal.

The speaker icon only indicates the priority of playing audio from any camera and not for sound detection notification.

The Split screen prioritizes audio from the camera on the LEFT side of the Parent unit screen. If the LEFT camera is silent and the RIGHT camera has audio, the icon will switch to the RIGHT camera. The icon is still displayed on the left camera if both cameras are silent.